This invention relates to the method of reducing aqueous phase separation and improving emulsion retention capacity of an emulsion composition comprising a lubricant base oil containing molybdenum ester/amide and its combination with alcohol-based fuel, such as E85 fuel and water. E85 is an abbreviation for an ethanol fuel blend of 85% denatured ethanol fuel and 15% gasoline or other hydrocarbon by volume, although the exact ratio of fuel ethanol to hydrocarbon can vary considerably while still carrying the E85 label. The ethanol content is adjusted according to the local climate to maximize engine performance. ASTM D5798 specifies the allowable fuel ethanol content in E85 as ranging from 51% to 83%.
In recent years, use of alternative fuel has resonated with the consumers concerned about U.S. dependence on imported oil as well as the ever increasing price of gasoline. As an alternative fuel to gasoline, use of ethanol produced from biomass has increased in recent years for the internal combustion engine. With the introduction of ethanol in gasoline came the concern of water-phase separation. Water in gasoline can have different effects on an engine, depending on whether it is in solution or forms a separate water phase. While a separate water phase in a fuel can be damaging to an engine, a small amount of water in solution with gasoline should have no adverse effects on engine components.
Although ethanol will readily dissolve water, water will separate from blends of gasoline and ethanol when the solubility limit in ethanol is reached. The amount of water required for this phase separation varies with temperature. When phase separation occurs in an ethanol blended gasoline, the water will actually begin to remove the ethanol from the gasoline. Therefore, the second phase which can occur in ethanol blends contains both ethanol and water. In the case of four stroke engines, the water-ethanol phase may combust in the engine. This combustion can be damaging to the engine because the water ethanol phase creates a leaner combustion mixture. Leaner mixtures tend to combust at highest temperature and can damage engines and also results in reduced fuel economy. In addition, this water-ethanol phase will compete with the blended oil for bonding to the metal engine parts. Therefore, the engine will not have enough lubrication, and engine damage may result. Hence, maintaining emulsion stability of alcohol-gasoline mixed fuel with lubricating oil compositions is a primary concern. Inability to maintain stable emulsions, especially in the cold climate and small infrequent short distance driving cycles, leads to separation of an aqueous layer which results in corrosion of fuel tanks, fuel delivery systems and other critical components of the engine. Hence, any method to reduce aqueous phase separation will be useful.
A particularly useful friction modifier additive used in engine oils is a molybdenum ester amide, available as MOLYAN® 855 from Vanderbilt Chemicals, LLC, of Norwalk, Conn. While this molybdenum compound provides excellent friction modifier properties, it suffers from a drawback when used in engines running alcohol-based fuels, such as E85. In particular, the molybdenum ester amide compound used in such an engine may lead to unwanted aqueous phase separation in the fuel mixture. Accordingly, there is a desire to overcome this problem by formulating a lubricating composition which contains a molybdenum ester amide, but which avoids aqueous phase separation when used with E85 or other alcohol based fuels.
U.S. Pat. Application No. 20120108478 to Lam et al. discloses a lubricant composition suitable for use in engines fueled by gasoline or bio-renewable fuels, or both, comprising an oil of lubricating viscosity and a dispersant system to reduce aqueous separation in an emulsion composition. A dispersant system suitable for use herein can comprise at least one dispersant. Useful dispersants include, but are not limited to, basic nitrogen-containing ashless dispersants, such as hydrocarbyl succinimides; hydrocarbyl succinamides; mixed ester/amides of hydrocarbyl-substituted succinic acids, Mannich condensation products of hydrocarbyl-substituted phenols, formaldehyde and polyamines; and amine dispersants formed by reacting high molecular weight aliphatic or alicyclic halides with amines, such as polyalkylene polyamines. Mixtures of such dispersants can also be used.
Research paper published to Patel et al. (SAE Int. J. Fuels Lubr. 3(2):938-945, 2010) discusses the effect of viscosity index modifier on ethanol/gasoline/water emulsions formed in E25 and E85 fuels in passenger car motor oil. This study includes viscosity index modifiers such as olefin co-polymer (OCP), styrene-isoprene polymer (SI) and poly (alkyl methacrylate) polymer (PMA) at treat rate of 8.9 wt. %, 7.2 wt. % and 5.8 wt. % respectively. This study reported that none of the emulsion exhibited a separate water phase, regardless of the types of viscosity index modifier.
WO 2013/182581 relates to an engine oil additive for increasing fuel economy. The additive comprises a molybdenum compound, such as molybdenum ester amide (MOLYVAN® 855) in an amount which provides 1-1000 ppm (0.0001-0.1 wt. % Mo); a polyalkyl (meth) acrylate at 1-15 wt. %, preferably 2-8 wt. %; a phosphorus compound; and an antioxidant system. It is noted that the invention is specifically directed towards new fuel economy requirements for gasoline and/or diesel engines. There is no mention of E85 ethanol-based fuels, or their attendant emulsion problems.